Cup-shaped diaphragm for hydraulic forming press



Aug. 8, 1967 H, MQLLER 3,334,504

CUP-SHAPED DIAPHRAGM FOR HYDRAULIC FORMING PRESS Filed May 25, 1965United States Patent 3,334,504 CUP-SHAPED DIAPHRAGM FOR HYDRAULICFORMING PRESS Hugo 'Miiller, Trollhattan, Sweden, assignor to SaabAktiebolag, Linkoping, Sweden, a corporation of Sweden Filed May 25,1965, Ser. No. 458,673 2 Claims. (Cl. 72-63) This invention relates toimprovement in resilient diaphragms for hydraulic forming presses, and,more specifically, the invention concerns the type of cup-shapeddiaphragm which has a circumferential upwardly projecting side wall thatclosely fits in the lower portion of a bore in a pressure chamber memberof a hydraulic forming press, and which has a bottom wall that closesthe bottom of the bore and transmits force from pressure fluid in thebore to a sheet metal blank therebeneath, to cooperate with a formingtool in shaping the blank.

The side wall of a cup-shaped diaphragm of the type with which thisinvention is concerned mainly serves to provide a seal around the bottomportion of the bore in the pressure chamber member of the press, and issubjected to relatively little strain and wear when the diaphragm is inuse. But the bottom wall of such a diaphragm is subjected to very largestrains because of the flexing which it must undergo to accommodate theshape of the forming tool as the blank is formed over it.

Heretofore such cup-shaped diaphragms have been made in one piece, fromrubber or the like, and hence when the bottom wall of the diaphragm wasdamaged, the entire diaphragm had to be replaced. Because of therelatively complicated shape of a cup-shaped diaphragm, its replacementwas costly, and the comparatively short useful life of the diaphragm hadto be amortized over the number of parts that could be produced by it,with the result that production cost was high for each part.

It is the general object of the present invention to provide an improvedcup-shaped diaphragm for a hydraulic forming press that will bring abouta substantial reduction in the cost of forming each part produced on thepress.

In the attainment of this objective the pattern of strains imposed upona cup-shaped diaphragm has been given careful attention. Particularlywith forming tools used for deep drawing, the central portion of thebottom wall of the diaphragm is subjected to substantial axialstretchiug during each forming operation as it is displaced upwardlyinto the bore in the pressure chamber member of the press by the blankand forming tool. However, the peripheral portions of the bottom wall,which cooperate with a fiat blank holding ring beneath the marginal edgeportion of the blank, are subjected to a substantial degree of radialstretching. Thus the bottom wall of the diaphragm is subjected to severeand nonuniform streching forces, particularly in zones thereof thatproduce abrupt changes in curvature of the blank being formed in thepress. It is as a result of these stretching forces It lat suchdiaphragms heretofore had a limited useful With the foregoing in mind,it is an object of the present invention to provide a cup-shapeddiaphragm of the character described which has great durability, andmore particularly to provide such a diaphragm which comprises acup-shaped main diaphragm member having a bottom wall portion with aconfiguration that best accommodates the stretching forces to which itis subjected, and certain relatively simple and inexpensive bottom wallmembers which are detachably secured to the bottom wall portion of themain cup-shaped member to complement the same and which are adapted toreceive the major portion of the normal wear to which the dia- 3,334,504Patented Aug. 8, 1967 phragm as a whole is subjected in use: and to bereadily replaced when they are damaged or worn out.

More particularly it is an object of this invention to provide acup-shaped resilient diaphragm of the character described which is inthree parts, one of said parts including the side wall and a bottom wallelement and being relatively complicated and expensive but having anindefinitely long useful life, and another of said parts being intendedto receive the major portion of wear and to be relatively frequentlyreplaced, but being extremely simple and inexpensive.

In general, the above stated objects are attained by the provision of acup-shaped diaphragm comprising three parts that are readily detachablyadhered to one another, namely a main member having a circumferentialside wall and an inner bottom wall portion which is integral with theside wall and which has a substantially flat upper surface and aspherically concave lower surface, an intermediate member which isdetachably adhered to the undersurface of the inner bottom wall portionof the main member and which has a flat undersurface and a sphericallyconvex upper surface complementing the undersurface of the inner bottomwall portion, and a lower bottom wall member having substantially flatparallel top and bottom surfaces and which is flatwise detachablyadhered to the underside of the intermediate member.

With the above and other objects in view which will appear as thedescription proceeds, this invention resides in the novel construction,combination and arrangement of parts substantially as hereinafterdescribed and more particularly defined by the appended claims, it beingunderstood that such changes in the precise embodiment of thehereindisclosed invention may be made as come within the scope of theclaims.

The accompanying drawing, which illustrates one complete example of thephysical embodiment of the invention constructed according to the bestmode so far devised for the practical application of the principlesthereof, is a fragmentary vertical sectional view through a portion of ahydraulic forming press incorporating a diaphagm that embodies the tion:

In the drawing the numeral 5 designates generally a pressure chamberbody in a hydraulic forming press, only the lower portion of thatchamber being shown. Through the chamber body there extends a verticalbore 6 which is closed near its bottom by the cup-shaped resilientdiaphragm of this invention, which is designated generally by 7.

Beneath the pressure chamber 5 the press has, as is conventional, ablank holding ring 8 with a fiat upper surface, and a punch 9 which isencircled by the blank holding ring and which cooperates therewith toprovide a forming tool. During a forming operation, the marginal edgeportion of a sheet metal blank 10 is flatwise clampingly confinedbetween the blank holding ring 8 and the peripheral portion of thediaphragm, while the central portions of the blank and diaphragm aredisplaced upwardly into the bore 6 by the punch 9. Suitable mechanism(not shown) is provided in the press structure to produce the necessaryaxial motions of the pressure chamber 5 and blank holding ring 8relative to one another and the punch 9, and fluid is maintained underpressure in the bore 6 above the diaphragm to force the blank intoconformity with the shape of the forming tool.

In general, the diaphragm 7 comprises three resilient elements, namely acup-shaped main member 11 having a circumferential upwardly projectingside wall 12 and an integral inner bottom wall portion 13, anintermediate principles of the present invenof the main member and isadhered thereto, and a lower bottom wall member which underlies theintermediate wall member and is adhered to the latter.

The assembly constituting the cup-shaped diaphragm 7 is secured in thelower portion of the bore 6 by means of a circumferential radiallyoutwardly projecting ridge or land 16 on the side wall 12, spaced ashort distance below the rim thereof, which is received in a closelyfitting circumferential groove 17 in the bore 6. An internal clampingring 18, confined within the side wall portion of the diaphragm, inradial alignment with the land 1.6, maintains radially outward forceupon the side wall to hold the land 16 seated in the groove 17 and thusprevent axial displacement of the diaphragm.

The lower portion of the diaphragm assembly 7 has a reduced outsidediameter and is surrounded by a resilient sealing ring 19 which isdisplaceable both radially and axially to some extent by reason of itsresilience. The lower portion of this sealing ring has a smaller outsidediameter than its upper portion to define on the sealing ring anexternal downwardly facing circumferential shoulder 20. A small radiallyinwardly projecting circumferential land or ridge 21 in the bore 6, nearthe lower end thereof, defines an upwardly facing shoulder against whichis seated the shoulder on the sealing ring, and by which the sealingring is thus held in place The purpose of the sealing ring is to obviatethe need for an extremely close fit between the forming tool and thebore 6 which the forming tool is adapted to enter, all as moreparticularly explained in the copending application of Hugo Moller, Ser.No. 458,672, filed May 25, 1965, to which reference may also be made foradditional details concerning the press herein referred to.

The bottom wall portion 13 of the cup-shaped main diaphragm member 11,which comprises the inner wall portion of the diaphragm assembly, has,when in its unflexed condition, a substantially flat upper surface 22and a spherically concave bottom surface 23; and hence it is thinnest atits center and has increasing thickness toward its periphery. Theintermediate wall member 14 has a spherically convex upper surface 24which complements the concave underside of the inner wall portion, andhas a flat undersurface 25; hence the intermediate member is thickest atits center and tapers in thickness toward its periphery. The lowerbottom wall member 15 has flat, parallel upper and lower surfaces 26 and27, respectively, and is thus of uniform thickness across its diameter.It will be noted that the three wall elements 13, 14 and 15, whenadhesively joined to one another, cooperate in defining a bottom wallfor the diaphragm which is of uniform thickness across its diameter andwhich, in unfiexed condition, has flat, parallel top and bottomsurfaces.

In the formation of a sheet metal part by means of any cup-shapeddiaphragm, the greatest strains on the diaphragm occur, as explainedabove, in the peripheral portion of the bottom wall, in the neighborhoodof its junction with the side walls; and it will be observed that thebottom wall portion 13 of the main body member 11 in the diaphragm ofthis invention has its greatest thickness in this region of greateststrain. The intermediate wall member 14 is subjected to strains whichincrease the value toward its center Where it has its greatestthickness. The lower bottom wall member 15, which is in direct contactwith the sheet metal blank being formed, and which therefore receivesthe most wear, is the least expensive of the three members comprisingthe diaphragm, by reason of its flat parallel upper and lower surfaces,which enable it to be cut from suitable sheet material.

Of course the lower bottom wall member 15 needs the most frequentreplacement of the three elements comprising the diaphragm of thisinvention, but since it receives all of the normal wear imposed upon thediaphragm, and is very inexpensive, diaphragm costs per part produced isrelatively very low. The intermediate bottom wall member 14 normallydoes not need replacement, but it sometimes happens, in the formation ofparts having complicated shapes, that a sheet metal blank is splitduring the forming operation, and the sharp edges thus produced on theblank damage not only the lower bottom wall element 15 but also theintermediate member 14. Even in such cases, the cost of the two damagedmembers is substantially less than the cost of an entire cup-shapeddiaphragm of prior unitary construction.

From the foregoing description taken together with the accompanyingdrawing it will be apparent that this invention provides a cup-shapeddiaphragm for hydraulic forming presses which achieves a comparativelylow diaphragm cost per formed part by reason of its comprising threemembers, the most expensive of which is of pratically indefinite usefullife, while the member which receives almost all of the normal wear, andthus needs most frequent replacement, is very simple in shape andtherefore low in cost.

What is claimed as my invention is:

1. A resilient substantially cup-shaped diaphragm for a hydraulicforming press, of the type having a circumferential upwardly projectingside wall which closely fits in the bottom portion of a downwardlyopening bore in a pressure chamber member of a press, and a bottom wallfor closing the bottom of said bore and for transmitting to a sheetmetal blank therebeneath force exerted by pressure fluid in the bore,wherein said bottom Wall of the diaphragm is characterized by:

(A) an inner resilient wall portion integral with said circumferentialside wall, said inner wall portion being thinnest at its center andincreasing in thickness toward its periphery;

(B) an intermediate resilient wall member having an upper surface whichis complementary in shape to the undersurface of the inner wall portionand which is detachably adhered thereto, said intermediate wall memberbeing thickest at its center and tapering in thickness toward itsperiphery; and

(C) a lower most wall member which is of uniform thickness at all pointsthereacross and which has its upper surface complementary in shape tothe undersurface of the intermediate wall member and detachably adheredthereto.

2. A resilient substantially cup-shaped diaphragm for a hydraulic press,of the type having a circumferential upwardly projecting side wall whichclosely fits in the bottom portion of a downwardly opening bore in apressure chamber member of a press, and a bottom wall for closing thebottom of said bore and for transmitting to a sheet metal blanktherebeneath force exerted by:

(A) an inner resilient wall portion which is integral with saidcircumferential side wall and which, when unflexed, has a substantiallyflat upper surface and a substantially spherically concave undersurface,said inner wall portion having its least thickness at the axis of thediaphragm;

(B) an intermediate resilient wall member having a substantially fiatundersurface and a spherically convex upper surface which iscomplementary to the under surface of the inner wall portion anddetachably adhered thereto; and

(C) a lowermost resilient wall member having substantially flat,parallel top and bottom surfaces and having its top surface detachablyadhered to the undersurface of the intermediate wall member.

References Cited UNITED STATES PATENTS 2,878,767 3/1959 Paulton 72633,033,143 5/1962 Grankowski 7263 FOREIGN PATENTS 875,364 6/1942 France.

CHARLES W. LANHAM, Primary Examiner.

K. C. DECKER, Assistant Examiner.

1. A RESILIENT SUBSTANTIALLY CUP-SHAPED DIAPHRAGM FOR A HYDRAULICFORMING PRESS, OF THE TYPE HAVING A CIRCUMFERENTIAL UPWARDLY PROJECTINGSIDE WALL WHICH CLOSELY FITS IN THE BOTTOM PORTION OF A DOWNWARDLYOPENING BORE IN A PRESSURE CHAMBER MEMBER OF A PRESS, AND A BOTTOM WALLFOR CLOSING THE BOTTOM OF SAID BORE AND FOR TRANSMITTING TO A SHEETMETAL BLANK THEREBENEATH FORCE EXERTED BY PRESSURE FLUID IN THE BORE,WHEREIN SAID BOTTOM WALL OF THE DIAPHRAGM IS CHARACTERIZED BY: (A) ANINNER RESILIENT WALL PORTION INTEGRAL WITH SAID CIRCUMFERENTIAL SIDEWALL, SAID INNER WALL PORTION BEING THINNEST AT ITS CENTER ANDINCREASING IN THICKNESS TOWARD ITS PERIPHERY; (B) AN INTERMEDIATERESILIENT WALL MEMBER HAVING AN UPPER SURFACE WHICH IS COMPLEMENTARY INSHAPE TO THE UNDERSURFACE OF THE INNER WALL PORTION AND WHICH ISDETACHABLY ADHERED THERETO, SAID INTERMEDIATE WALL MEMBER BEING THICKESTAT ITS CENTER AND TAPERING IN THICKNESS TOWARD ITS PERIPERY; AND (C) ALOWER MOST WALL MEMBER WHICH IS OF UNIFORM THICKNESS AT ALL POINTSTHEREACROSS AND WHICH HAS ITS UPPER SURFACE COMPLIMENTARY IN SHAPE TOTHE UNDERSURFACE OF THE INTERMEDIATE WALL MEMBER AND DETACHABLY ADHEREDTHERETO.